Note "detain" is not the same as "punch in the face and knock to the ground". To detain is to prevent from leaving, preferably while causing the minimum needed level of damage to the detainee consistent with officer safety. The officer evidently failed to accomplish this last part, hence his firing.
<> hence his firing.<>
Well about that firing:
“Before everyone starts applauding, what Ramsey has done is to ensure this officer will not only get his job back, but also get back pay for the time he is off. Ramsey did the same move with a group of officers when he first arrived and they were all reinstated. Ramsey knows this. What he is actually doing is ensuring this officer doesn’t lose his job for more than a year or so. The FOP is right on this. When a lawsuit is filed the City will lose. For short term good press Ramsey is throwing away the greater long term good. The officer can be successfully fired if the right procedures are followed.”
— Philly Senior Posted 5:50 AM, 10/04/2012